1. Field of the Invention
The present invention relates to a double-sided organic electroluminescent display having an optical shutter, and to an information terminal using the same.
2. Discussion of Related Art
Generally, electroluminescence (EL) is a phenomenon that an exciton is created by an electron and a hole respectively injected from a cathode and an anode into one of a monomer inorganic layer, a monomer organic layer, a polymer inorganic layer, and a polymer organic layer, and emits light of a predetermined wavelength. The EL is classified into an inorganic EL and an organic EL according to materials.
The inorganic EL device is observed in a thin film type structure basically comprising an upper insulating layer, a lower insulating layer, and a fluorescent layer formed therebetween, or in a thick film type structure comprising a reflecting layer having an insulating material, and an insulating binder having a fluorescent material.
However, an EL device using the inorganic EL is characteristic of low brightness and low efficiency, and therefore is not suitable for application of a display. Thus, the EL device using the inorganic EL should be improved in its characteristic.
The organic EL device emits light when an exciton is transferred from an excited state to a ground state, wherein the exciton is created by combination of an electron and a hole respectively injected from a cathode and an anode into a light emitting layer. Such an organic EL device is employed in a flat panel display and allows the flat panel display to have advantages of low voltage drive, low power consumption, high brightness, self-illumination, fast response speed of several microseconds, wide-view angle, lightweight, thin thickness, low production cost, etc., so that it has been rapidly developed.
However, in the conventional double-sided organic EL display, opposite electrodes of the organic EL device are formed of the transparent electrodes. Therefore, while a user sees an image displayed on one side screen, the light transmitted through the other side screen makes it difficult to correctly see an image displayed on the screen.
Further, in an information terminal such as a mobile terminal, which comprises the conventional double-sided organic EL display, visual recognition of the display is easily affected and deteriorated by circumferential luminous intensity. For example, when the circumferential luminous intensity is relatively high, it is difficult to see an image displayed on the display panel of the mobile terminal.
Also, in the conventional information terminal, even though a user increases the brightness of the display panel when the circumferential luminous intensity is relatively high, the visual recognition is not enhanced. For example, when the conventional foldable mobile terminal comprising the double-sided organic EL display is used in daylight or in a bright place, the double-side of the image displaying part is exposed to bright light. Accordingly, it is difficult for a user to recognize the information displayed on the display panel even though a user increases the brightness of the display panel.
Thus, in the conventional double-sided organic EL display and the information terminal such as a mobile terminal using the same, visual recognition can be deteriorated by circumferential luminous intensity.